The Heart and Science of Parenting

Bottle-feeding and Obesity Risk

by Alice Callahan on May 25, 2012

Source: Wikimedia Commons

A study published this month in Archives of Pediatric and Adolescent Medicine looks at the relationship between infant feeding practices and weight gain (1). Breast milk vs. formula? Nope, it isn’t that simple.

Led by Dr. Ruowei Li of the CDC, this prospective longitudinal study tracked feeding and weight gain in 1900 infants during their first year of life. Each month, mothers were asked how they fed their babies in the last 7 days, and from their replies, infants were grouped into the following categories across ages:

Breastfed only

Breastfed and human milk by bottle

Breastfed and formula by bottle

Human milk by bottle only (i.e. exclusive pumping)

Human milk and formula by bottle

Formula by bottle only

The mothers in this study were mainly white, married, and had at least a high school education. A third were on WIC. About 50% were overweight or obese. Statistical methods were used to adjust the findings for a range of maternal factors, including BMI, as well as infant sex, gestational age, birth weight, and age of solid food introduction.

The most important finding from this study was that infants fed by bottle only – whether fed formulaor breast milk – gained more weight than those fed breast milk at the breast. Formula-fed infants gained an additional 71 grams (P<0.001), and babies exclusively fed breast milk by bottle gained an additional 89 grams (P=0.02) per month. Babies that were breastfed and given breast milk by bottle did not have increased weight gain.

Many earlier studies have found that formula-fed infants grow faster than breastfed infants. (I’ve written before about the importance of using the WHO growth charts instead of the CDC charts for breastfed babies, for this very reason). Studies have also found an association between formula-feeding and risk for obesity later in childhood, although it is not clear if this is a causal relationship (2). There are a range of hypotheses to explain these observations. Is it biological – something in the milk, like the hormones found in breast milk but not formula? Or is it behavioral – the act of breastfeeding itself?

The data from this study support the idea that the differences in weight gain are at least in part due to feeding behavior. The babies that were fed by bottle gained the most weight, and this was true whether they were fed formula or breast milk. I can guess how this happens. If you are feeding a baby a bottle, then you have prepared a particular amount, and it is hard to not hope that the baby will finish it. Particularly if you have gone through the labor of love of pumping that milk, then you are probably especially invested in seeing your baby polish off the entire bottle. Even if baby is showing some signs of being full or drifting off to sleep, you might gently encourage her to drink just a little more. By doing so, you’re over-riding baby’s natural sense of satiety.

What is needed is a randomized trial with an intervention teaching moms and dads to read and respond to baby’s hunger and satiety cues. If bottle-fed babies in this group showed slower weight gain, similar to breastfed babies, then we’d know that feeding behavior mattered to weight gain. This kind of research is important. The more we understand about the mechanisms behind differences in bottle and breastfed babies, the more information we have to help parents give their babies the best start, regardless of how they are fed.

There is an alternative explanation to these data. During each breastfeeding session, the composition of breast milk changes, with fat content being higher in the hindmilk (at the end of the session) than the foremilk. This could give a signal to the breastfeeding baby that it is time to wrap things up. These compositional changes don’t occur when baby is fed a bottle of pumped breast milk.

Some further caveats to these findings: First, we don’t really know if faster weight gain during the first year actually causes increased risk of obesity or has any other negative effects. Second, the number of babies fed breast milk exclusively by bottle was relatively small, but this group is what makes this study so interesting. And finally, a small group of babies fed both breast milk and formula by bottle did not gain more weight, making interpretation of the findings just a little sticky.

I don’t consider this study to be conclusive by any means, but it sure is interesting. It is a reminder that no matter how you feed your baby, it is important to pay attention to her cues and let her take the lead on how much and how often to eat.

P.S. – Since I was on a Facebook fast last week during our trip to Sedona, I have no idea if this study was a big topic of conversation. So I apologize if it is old news, but it was one of the few papers I printed out to bring on our trip, and it was the only one I actually read what with all the sleep deprivation and recreation.

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Makes sense to me, intuitively. We had to supplement a bit with formula at some points, and gave my son bottles of pumped breastmilk while I was at work. In both cases, we found that he sucked down his bottles really fast. We tried really hard to slow him down– super slow flow nipples, frequent pauses, upright position, small servings, just like Kellymom.com recommends, but he still would slam down a lot more milk in a bottle than from the breast, as far as we could tell, and a lot faster too. It was just so much easier for him to get it out (he had sort of a weak latch, milk transfer issues).

We also had to bottle feed our daughter breastmilk while I was working, and we noticed she also sucked down the bottles very quickly despite using the slowest flow and most difficult style of bottle we could find. Nursing has so many built in mechanisms for slowing milk consumption (baby has to wait for let down, baby has to wait for second let down, etc!). Our daughter is currently 8% weight range on the WHO chart, and received only breastmilk from a bottle about 70% of the time on a normal work day. I’m certain proper training about bottle feeding could reduce the obesity rate. I still recall when our daycare asked me to send 18oz of breast milk per day for a child who I knew only needed 9 oz. They made this request because of my daughter’s age, and the state’s legal requirements. We immediately went and got a doctors not explaining she would not get more than 9 oz in a 9hr work day.

I have a theory. Suckling from the breast requires significant effort by the baby. It has long been considered that bottle feeding is easier than breast-feeding but vented, so called ‘anti-colic’ bottles are the easiest of all. Because the negative pressure inside these bottle is relieved by an air inlet valve , there is nothing to pull against. Consequently, milk is delivered almost free-flow. Mums using anti-colic bottles often report that their babies guzzle, or are swamped, with milk running down their chins. They are taking too much, too fast, before the food value satiates the baby’s hunger. I think this is compromising the instinct to stop when full and this contributes to over-feeding. This can’t be good for setting good eating habits for the future!

As always, fascinating. I wonder about the caloric expenditure of bottle vs. breast feeding as well. One of the simultaneously cool and frustrating parts of following the biomedical literature is the apparently contradictory findings that multiple studies generate.

Hmmm, your question of caloric expenditure is really interesting. I wouldn’t be surprised if there was a small difference, since babies do seem to be able to finish a bottle feed so much faster. And yes, interpreting these studies is tricky, and gleaning something that we can use in practice usually requires stretching the interpretation a bit, I freely admit:)

In addition to teaching parents how to watch baby’s cues when bottle-feeding, it should be noted that bottle-fed babies are often fed by many different people. Childcare providers, relatives, siblings, friends, etc. It can be frustrating watching your mother-in-law encourage your baby to finish a bottle. Most people seem to think you’re obsessive or worry too much if you make an issue of it, because they don’t understand. And most often, when someone else is feeding your baby, you aren’t there watching.

Great point, and I agree that navigating that line between sticking up for something you think is really important and seeming overbearing can be very tricky. At the same time, I used to do a lot of baby-sitting, and I can remember feeling like it would look bad if the baby didn’t finish the amount of milk that the parents said she would drink. It would have gone a long way towards helping me relax if I was told, “She may drink anywhere from x to x ounces, but if she seems full, don’t try to make her drink more.”

Really interesting post. We’ve struggled with the growth chart thing; my little one is always on the lower end; but she has been exclusively breastfed and has my petite sized genes I think. My other friends who exclusively breastfeed have also noted the same thing with their little ones. Good to hear some research supporting this phenomenon.

BabyC is small, too. She was born big but quickly settled into the 5-10% range by the time she was 6 months. I’m sure this is just one of many factors involved, but it is nice to see data like these, I agree.

All good points from the other commenters. I recall one time when I went out, the babysitter had to give my son some breastmilk I’d expressed. She ended up using 3 lots (equivalent to 3 feedings) and in one sitting demolished my precious supply of ‘spare’ milk! That being said, he was the only of my 3 kids to take a bottle (even with breastmilk in it), and is by far the tiniest. So there you go.

On the other end of the spectrum, my mother said she deliberately overfed me (as she’d had so much difficulty getting my older sister to gain weight so she was doing it from a good motive), and I was a truly huge baby at one point. You know the type, with multiple sumo-style rolls in each thigh. Thankfully I’m not still at that end of the spectrum now, so I think it is good to remember that big baby does not always equate to big adult.

Always good to get some real-world stories to put the study into perspective! I’m interested in learning more about how much early weight gain truly matters. We’ve all seen those sumo babies that slim down within a year or two, and I don’t know that there are long-term concerns with that, but again, it isn’t something I’ve researched extensively (yet!)

Great summary. Your first caveat was exactly the same as what I was thinking as I read the description of the study’s findings. As ever when I read about this topic, I wish there were no such thing as breastfeeding so that this wouldn’t be such a difficult and emotionally-charged issue for most mothers. Having facts helps some, and for others just makes them feel guiltier if they can’t or don’t breastfeed.

Jessica, thanks for your comment. I know that this is a tough topic for many moms, and I wish feeding choices/realities didn’t carry so much guilt and anxiety. But as a mom and a scientist, I think this type of work is important (although we only learn so much from any one study, this one included). Breastfeeding is the best model we have for feeding infants, because it has evolved with our species. The better we understand it, the more we will be able to help moms who struggle to breastfeed and develop formulas that come closer to providing the benefits of breast milk. One thing I thought was cool about this study is that it implies that part of the gap in weight gain between BF and bottle-fed babies is modifiable by a change in behavior. It may not be an intangible, mysterious property of breast milk, it may be something that formula-fed babies can benefit from simply by encouraging the caregiver to tune into baby’s cues more and forget how much milk is left in the bottle (easier said than done in my experience!).

Well…i have two children. the first one due to difficulties did not breastfeed and she was always a tiny baby. My son, my second baby was (is) breastfeed and is actually a giant compared to her. an example, she was 7.5 kg (16.5 pounds) at the 6th month appointment while he was 9.5kg (20.9 pounds). And with her i had started cereal at 5 months while with him we started later. It may be that he is a boy and she is a girl but the difference is noticeable, it is only the breastfeeding but the rest is the same. One thing though breastfeeding or not both babies ate and eat vegetables without any problem.

So very important to remember that the feeding relationship has a huge impact on the child”s future relationship with food. One mother had no physical problems but so disliked breastfeeding that she was uncomfortable and baby was unhappy. When they switched to bottles she relaxed and became far more closely attuned to what her baby wanted. Feeding time became much more close and loving. One thing that just can’t be tested with randomized clinical trials is the quality of that attunement.

Very interesting read. Maybe more so for me since I exclusively pump and yet our Little Miss is in the lower growth range. Although, it could be due to the fact that I produce more than enough milk that there’s no stress for me about having more ready if she decides not to finish a bottle or spits it all up. Thanks for the info, appreciated and I’m going to direct a friend here to read as well!

I know I’ve arrived at this discussion late, but I feel compelled to reply anyway. :-) Unfortunately, despite all best efforts, I had to formula feed my baby. I just didn’t have the milk supply myself, despite obsessive pumping, downing gallons of Mother’s Milk Tea, supplementing with Goat’s Rue, and visiting weekly with a lactation doctor for nearly 4 months. So, my son gets formula. He was on the high end of the growth charts at birth (8 lbs, 3 oz and 21.5 inches) and for his first couple of pediatrician visits. Then, at his four month visit, his height remained at 90% while his weight dropped down to 25%. The doctor instructed us to ensure that he is getting 32 oz of formula every day, plus solids. Being a concerned and obedient parent, I began hassling my son to get his 32 oz down everyday, plus added in oatmeal and fruits and veggies. I worried constantly about failure to thrive. At his 6 month check-up, his weight remained in the 25th percentile and now the doctor has us upping his intake of solids in addition to all the formula. I tried to explain that, first of all, he isn’t that hungry, and, second of all, he is following the exact same growth pattern that his father followed as an infant so it is probably just genetic. She dismissed both of these explanations and just told me to get him to eat. So, if there is a link between formula and obesity, I can’t help but wonder if it is not the formula or the bottles, but the fact that the amount of ounces fed is tracked so closely combined with failure to consider genetics and an inability to properly understand the growth charts. The first question asked at every doctor visit is whether we are formula or breast feeding. When we answer formula, we are then asked to report how much. This puts too much emphasis on the quantity and not enough on all the other variables that need to be considered.

Marie, thanks for sharing your story, and I think you might be onto something. I wonder if pediatricians are less likely to react to changes in growth patterns with breastfed babies vs. formula-fed babies. I would honestly consider finding another pediatrician or just being prepared to disregard her feeding advice – which isn’t a great option considering that we could all use some trusted support with regards to feeding. I highly recommend “Child of Mine: Feeding with Love and Good Sense” by Ellyn Satter. I teach a Family Food and Nutrition class and use this as one of our texts – plus I have found it very useful in my own parenting. I love that she talks about bottle-feeding dynamics a lot, and she emphasizes listening to your baby’s cues above all else. Your baby knows how much food is right for him. How on earth could we know better than him how much his body needs? When we disregard his cues early in life, he learns to disregard his own cues of hunger and satiety, which are vital for a healthy relationship with food throughout life. You know all this – that’s why you’re bothered by your pediatrician’s advice. I’d follow your son’s lead:)

My daughter was exclusively breastfed and dropped from 95th percentile for weight at birth to 5th by 9 months. She’s stayed between 5-10% ever since. I’m not saying that this pattern is healthy for all babies, but based on her genetics and her eating, I do think that she’s grown into the body that is right for her.

The problem is everyone LOVES a chunky baby and thinks that its healthy for them. I dont like using those ‘growth charts’ because they are still very inaccurate since the only studies done to make the charts are by mothers who breastfeed and do not smoke. Not everyone breastfeeds and i’m sorry but not every mother doesn’t smoke either despite what they are told (I am a non smoker though.. just making a point). And what about charting formula fed babies so they have their OWN chart and not try to compare them to Breastfed babies?

Honestly? I measure and weigh my child myself, document her growth on my own charts and I will use those charts for future children. If something changes between kids 1-2 then the 3rd one will be off the second set of charts…. if something else changes use the more up to date charting system you have. Also DO YOUR OWN HOMEWORK! LISTEN TO YOUR INFANTS CUES AND GO WITH YOUR GUT. Not every doctor knows best. Some will just throw something at you and send you on your way out with your head spinning.

I believe doctors contribute to a lot of the obesity in infants because they want to see a chunky baby and make sure they are in the upper percentile and, if like mine, will tell you to continue to feed your infant more formula even if she is 3 months old and consuming 8 oz bottles every 3 hours.

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I'm Alice Callahan. I'm trained as a research scientist and have a PhD in Nutrition. I use my background in science to investigate parenting questions and find evidence-based answers. No mommy wars here - just science, and empathy and respect for one another.

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